Sustained casing annulus pressure (SCP) due to the influx of pressured liquids or gases, water or hydrocarbon, from unknown points of entry and at unknown depths is a large-scale problem and presents safety hazards and regulatory concerns in the oil and gas industry. It is estimated that over 8,000 wells and 11,000 annuli are affected in the offshore Gulf of Mexico Region. A failure to control the casing annulus pressures below maximum allowable limits may result in a well blowout or other uncontrolled event that may result in significant loss of property, environmental impact, and potentially loss of life.
The injection of high-density brine solutions into the casing annulus has typically been used to control the casing annulus pressure. However, injecting or displacing denser fluids into the casing annulus of a well, without having to undergo significant well operations is difficult. The principle difficulty arises from the fact that often the casing annulus space, into which the fluid must be injected, is sealed on both ends and may be an inner or outer string without access other than through a valve on the casing head or spool. This makes the displacement of the existing fluid in the casing annulus space very difficult.
Current technologies often rely upon the systematic injection and bleed off of small amounts of brine fluid resulting in the over dilution of the more dense brine fluid. As the more dense brine fluid is injected and begins to drop through the less dense fluid, it also begins to disperse and mix with the less dense fluid; the hydrostatic pressure in the casing may thus increase somewhat due to the injection of the more dense brine into the casing annulus, but the more dense brine will not have dropped all the way to the bottom of the well; therefore, when it is time to bleed off fluid from the top to permit additional more dense brine to be injected, some of the more dense brine injected previously is dispersed in that which is bled off. Also, now the density of the fluid at the top of the casing is more dense than it was before, therefore the next injection of more dense brine will be attended with a slower rate of falling through the increasingly more dense top fluid and a greater degree of dispersion of the one into the other. Eventually this process of injection and bleedoff becomes self-limiting, often without increasing the hydrostatic pressure within the casing annulus enough to bring the casing pressure under control or even to keep up with the rate of increase in pressure. Injection tubes can be inserted to direct the injection of more dense brine slightly below the surface. However, these injection systems have not produced consistent results.
Thus, there exists a need for a top down process to introduce dense fluid, which is effectively immiscible, and drops without dispersing to the bottom of the annulus, efficiently displacing the less dense fluid, and raising the pressure in the casing annulus to the point where the pressure within the casing annulus is equal to or greater than that of the influx of fluids or gases, water or hydrocarbon, that had been bleeding into the annulus previously.